A typical mobile communications network (NW) comprises a radio access subsystem having base stations and equipment for controlling the base stations, and mobile terminals, referred to as user equipment (UE). In this environment, receiver diversity has become an important feature for the UE as the UE must support high data rates, such as High Speed Downlink Packet Access (HSDPA). Receiver diversity, which is generally defined as a wireless device architecture with multiple separated receive paths, increases mobile communications network data capacity and performance.
Having multiple (e.g., at least two) antennas and corresponding receiver chains in a UE, working independently of each other makes it possible to perform inter-frequency (IF) or inter-Radio Access Technology (RAT) measurements (collectively referred to herein as IFM) for mobility management, without switching into compressed mode in the WCDMA case.
In compressed mode, the data transmission is interrupted so that the UE can change the carrier frequency and perform measurements at regular intervals. To achieve a lossless transmission, data is compressed and transmitted during a shorter time period. This may introduce reception gaps where IF measurements can be performed. In other words, to enable a UE to perform radio measurements on a frequency other than the frequency in use for the current call in connected mode using a dedicated physical channel, a compressed mode is used. In compressed mode, the data transmission is interrupted during a given time interval to allow the UE to perform measurements, and the data rate is increased outside the time interval to compensate for the transmission gap. Compressed mode results in a capacity loss of half of a frame such that a transmission gap of the remainder of the frame is introduced that could be used for IFM. For example, in WCDMA compressed mode frames, the spreading factor is halved and the base station transmit power is doubled.